STUDY OF CEI,L MECHANICS 447 



MONASTER EGGS 



Although monaster eggs were known long before, Boveri 

 seems to have been the first to realize the value of such eggs 

 in analytical studies of cell dynamics and both he and his wife 

 published papers dealing with the external behavior of the 

 eggs (Th. Boveri, '03), and the behavior of chromosomes, cen- 

 trosomesand other cell parts (M. Boveri, '03). Neither of these 

 authors, however, had undertaken a study of the movements 

 of the protoplasm which are such a conspicuous feature of 

 monaster eggs; especial attention was therefore given to this 

 in the present work. 



A great variety of agents act upon the normal sea urchin 

 eggs in such a way that only one division center appears when 

 the division cycle is initiated. Numerous chemicals produce 

 monasters, strychnine (Hertwigs, '87), MgCl 2 (Wilson, '01 a), 

 carbon dioxide (Herbst, '14). Many narcotics do the same. 

 Chloral hydrate (Hertwigs, '87), ether (Wilson, '01 b), phenyl 

 urethane (Painter, '15). Mechanical stimuli act often in the 

 same way. Thus Boveri found that by shaking eggs a few 

 minutes after fertilization, a good percentage of monaster eggs 

 often resulted. 



The last named method was employed, as it was the simplest, 

 and introduced no additional factor, such as the use of chemicals 

 might have done. As soon as the fertilization membrane ap- 

 peared, in eggs artificially fertilized, they were placed in a test 

 tube, with as little water as possible and shaken violently by 

 hand for twenty seconds. Precaution was taken to keep 

 the warmth of the hands from increasing the temperature of 

 the eggs, and after shaking they were placed in shallow dishes 

 and allowed to develop. 



The production of monasters is capricious and seems to 

 depend as much upon the condition of the eggs themselves as 

 on any other factor. If one treats two sets of eggs from dif- 

 ferent females in just the same way, shaking the same amount 

 and at the same time, in one set one may get ten per cent mon- 

 asters, and in the other only a few or none at all. Experiments 



